1. Field of the Invention
The present invention relates to a stepping motor of the hybrid type, and more particularly, to a stepping motor of the hybrid type having an improved structure in which there are provided coils having a high-density winding, which can be easily wound and mounted on the motor and thus can be produced at a low cost, and furthermore in which an abrupt change in the magnetic flux is obtained which leads to an increase in the torque.
2. Description of the Related Arts
In a known stepping motor of the hybrid type, as shown in FIG. 1, a revolving shaft 1 is fitted in a pair of bearings 2, 3 located at either end a casing 4 in such a manner that the revolving shaft 1 can freely rotate. A stator yoke 6 including a stator yoke 5 and having a ring shape in general is disposed on the inner wall 4a of the stator case 4. A plurality of stator teeth 7 are formed on the inner wall of the stator yoke 6 at predetermined intervals in a circumferential direction. Between the bearings 2 and 3, there are provided first and second ring-shaped rotor yokes 9, 10 formed in an integral fashion wherein the first and second ring-shaped rotor yokes 9 and 10 are separated from each other via a magnet plate 8 in the axial direction. A plurality of rotor teeth 9a and 10a are formed on the periphery of each rotor yoke 9, 10. The respective rotor yokes 9 and 10 form magnetic poles with polarities opposite to each other. In this structure, the rotor yokes 9, 10 can rotate in a stepping fashion in response to a driving pulse supplied to the stator coil 5 from a driving circuit (not shown).
The conventional hybrid type stepping motor having the structure described above has the following problems.
In the case of a stepping motor having the above-described hybrid structure in which a magnet plate is located between two rotor yokes, stator coils are wound around the respective teeth located inside the casing. However, in this structure, it is difficult to wind a coil around each tooth. Therefore, a high density of coil winding cannot be realized. Furthermore, the torque is not high enough when used as a D/D motor.